Well, when I was a kid and started to understand the stereo audio, I was curious how a single
needle can transfer two signals. I was a rookie (and still I am) and some pathetic maths like
L+R or L-R didn't meant anything to me... Ah, my youth...
Anyway, maths can't be heard but I was listening to the damn real thing! Yes, there were two
channels. I was freaked. WHERE IS THE SECOND NEEDLE?????
The groove has two walls so it can carry two signals; each one on every side. But how can these
signals be transferred using only one medium? The big bang in my head did happened when I
studied how a single wire can transfer multiple analog signals. It all depends on the point of
reference. WHAT???
Oh, yes.... The needle is one but it can be moved in different ways depending where the point
of reference is. So, the needle can be moved simultaneously in two ways, each direction
corresponding to one channel.
The above schematic shows a basic construction of an MM cart. It shows the stylus with the
magnet, the coils and the groove. Well, it's not state of the art but it can be used to our
purposes, here.
We take a signal on the right channel (marked with red color). This wave pushes the needle
not directly up and down but in an angle of 45° from the vertical axis. This results in the magnet
moving to the opposite direction but on the same plane of the 45°. On the back side of the
cart rest the two coils. Each one for every channel. They are placed with their gaps facing the
magnet in 45° from vertical axis and 90° from each other. Now, HERE IS THE MAGIC!!!
And the magic obeys to Faraday's law. The magnet moving from one pole of the coil's gap
to the other, produces emf (electromotive force). In simple words, it makes current flow through
the coil. The magnet moving vertical to the coil's gap (meaning that everytime it's distance
between both gap's poles is always equal) produces theoretically zero emf. Practically, for
technical reasons always some current is induced and this is the reason LP format has quite
poor channel separation.
In the drawing above, we can see a right channel signal. The opposite happens for a left
channel signal. A mixed movement represents a stereo signal.
Do you want more? The above configuration actually works flawless for the old mono records.
Indeed, a mono signal can move the needle only vertically inducing the same current in both
coils, so a perfect backwards compatibility. Clever?
PS. The above are not meant to substitute an advanced knowledge. The above are referring
to people like me who want to gain elementary knowledge.
PS No2. Not being a smart ass. Just my little contribution to the forum. I know novice people
are curious about the subject, just like I was.
I hope you'll find it useful.
Maky
needle can transfer two signals. I was a rookie (and still I am) and some pathetic maths like
L+R or L-R didn't meant anything to me... Ah, my youth...
Anyway, maths can't be heard but I was listening to the damn real thing! Yes, there were two
channels. I was freaked. WHERE IS THE SECOND NEEDLE?????
The groove has two walls so it can carry two signals; each one on every side. But how can these
signals be transferred using only one medium? The big bang in my head did happened when I
studied how a single wire can transfer multiple analog signals. It all depends on the point of
reference. WHAT???
Oh, yes.... The needle is one but it can be moved in different ways depending where the point
of reference is. So, the needle can be moved simultaneously in two ways, each direction
corresponding to one channel.
The above schematic shows a basic construction of an MM cart. It shows the stylus with the
magnet, the coils and the groove. Well, it's not state of the art but it can be used to our
purposes, here.
We take a signal on the right channel (marked with red color). This wave pushes the needle
not directly up and down but in an angle of 45° from the vertical axis. This results in the magnet
moving to the opposite direction but on the same plane of the 45°. On the back side of the
cart rest the two coils. Each one for every channel. They are placed with their gaps facing the
magnet in 45° from vertical axis and 90° from each other. Now, HERE IS THE MAGIC!!!
And the magic obeys to Faraday's law. The magnet moving from one pole of the coil's gap
to the other, produces emf (electromotive force). In simple words, it makes current flow through
the coil. The magnet moving vertical to the coil's gap (meaning that everytime it's distance
between both gap's poles is always equal) produces theoretically zero emf. Practically, for
technical reasons always some current is induced and this is the reason LP format has quite
poor channel separation.
In the drawing above, we can see a right channel signal. The opposite happens for a left
channel signal. A mixed movement represents a stereo signal.
Do you want more? The above configuration actually works flawless for the old mono records.
Indeed, a mono signal can move the needle only vertically inducing the same current in both
coils, so a perfect backwards compatibility. Clever?
PS. The above are not meant to substitute an advanced knowledge. The above are referring
to people like me who want to gain elementary knowledge.
PS No2. Not being a smart ass. Just my little contribution to the forum. I know novice people
are curious about the subject, just like I was.
I hope you'll find it useful.
Maky
